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            <h2 class="title"><a id="program"></a>Chapter 17.  Programmer Notes </h2>
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            <span class="sect1">
              <a href="program.html#program_appsignals">Signal handling</a>
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            <span class="sect1">
              <a href="program_errorret.html">Error returns to
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              <dt>
                <span class="sect2">
                  <a href="program_perfmon.html#program_perfmon_dtrace">Using the DTrace Provider</a>
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      <div class="sect1" lang="en" xml:lang="en">
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              <h2 class="title" style="clear: both"><a id="program_appsignals"></a>Signal handling</h2>
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        <p>
        When applications using Berkeley DB receive signals, it is
        important that they exit gracefully, discarding any Berkeley
        DB locks that they may hold. This is normally done by setting
        a flag when a signal arrives and then checking for that flag
        periodically within the application. Because Berkeley DB is
        not re-entrant, the signal handler should not attempt to
        release locks and/or close the database handles itself.
        Re-entering Berkeley DB is not guaranteed to work correctly,
        and the results are undefined.
    </p>
        <p>
        If an application exits holding a lock, the situation is no
        different than if the application crashed, and all
        applications participating in the database environment must be
        shut down, and then recovery must be performed. If this is not
        done, databases may be left in an inconsistent state, or locks
        the application held may cause unresolvable deadlocks inside
        the environment, causing applications to hang.
    </p>
        <p>
        Berkeley DB restarts all system calls interrupted by
        signals, that is, any underlying system calls that return
        failure with errno set to EINTR will be restarted rather than
        failing.
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